National Treasure: Book of Secrets

Five days after the end of the Civil War, John Wilkes Booth and Michael O'Laughlen, both members of the Knights of the Golden Circle, enter a tavern and approach Thomas Gates. They produce a diary containing an encrypted message, and entice Thomas, a well-known puzzle solver, to decode it. Thomas recognizes the message as using the Playfair cipher and begins to translate it. While he does so, Booth leaves for Ford's Theatre to assassinate President Lincoln. Thomas solves the puzzle, a clue to a treasure map, and realizes the men are still loyal to the Confederate cause and have a sinister motive for finding the treasure.

Unfortunately, he realizes this too late. O'Laughlen pulls a gun on him, threatening to shoot him if he does not hand over the diary, however he is distracted from Thomas when chaos erupts in the bar over news of Lincoln's assassination. Thomas rips several pages from the diary and throws them in the fireplace. The gunman shoots him and attempts to retrieve the pages, only succeeding in saving a fragment of a page. The dying Thomas gasps, "The war is over," but the man disagrees, stating, "You're wrong about that, the war has only just begun," and rushes from the bar. As he lies dying, Thomas tells his distraught son, Charles Gates, "The debt that all men pay…"

Over 140 years later, Ben Gates is telling his great-great-grandfather's story at a conference on Civilian Heroes to great acclaim until black market dealer Mitch Wilkinson shows one of the 18 missing pages of John Wilkes Booth's diary, with Thomas Gates' name on it, convincing everyone that Thomas was not only a conspirator, but the grand architect of the Lincoln assassination. Ben sets out to prove the innocence of his great-great-grandfather.